JP2012010541A - Control device of motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device of a motor which can achieve highly accurate speed control by preventing phase displacement in a high-speed region.SOLUTION: A control device comprises: a speed control system to generate a current command for a motor by performing a speed control according to a first control period; a current control system to generate an output voltage command for a power converter by performing a current control according to a second control period; means for converting the output voltage command and a current detection value into a coordinate by using an output voltage phase of the power converter; a latch signal generation part 21; an edge holding part 26; a rotation direction detection part 32; a rotation direction holding part 33; a time measuring counter 23; latches 25-1 to 25-4; an edge change information holding part 29; a CPU 30 to calculate a rotation speed by using the rotation direction, the measured time value and the edge change information; a counter 41 to count the number of at least one edge out of output pulse edges; a latch 42 to hold the counted value every second control period;and phase calculation means within the CPU 30 to calculate the output voltage phase from the counted value.

Description

  The present invention relates to a control device for driving an electric motor at a variable speed by a power converter, and in particular, has a function of calculating an electric motor speed and an output voltage phase of the power converter using an output pulse of an encoder attached to the electric motor. The present invention relates to a control device.

  An inverter is known as a device for driving an electric motor at a variable speed. Among the inverter functions, in order to control the motor speed with high accuracy, a speed adjustment function that detects the motor speed based on the output pulse signal of the encoder attached to the motor and makes the deviation from the speed command value zero. Some use it for control.

However, the number of pulses per rotation is usually determined for the output pulses of the encoder, and the density of the pulses varies depending on the rotation speed. In the low speed region where the pulse is rough, the detection accuracy is deteriorated and an error occurs in the speed detection value, which causes the speed control performance to deteriorate. When the speed control performance deteriorates, for example, in a crane, the speed control error becomes a ripple of torque, and vibration is transmitted to the load, which becomes a problem, or an error occurs in the stop position of the load during automatic operation due to the speed control error, Problems such as affecting other devices arise.
Further, the phase error of the output pulse is generated depending on how the encoder is attached, and in the detection method based on this output pulse, the influence of the phase error appears on the speed detection value, causing problems such as torque ripple as described above.

  Therefore, in order to solve the above-described problem, Patent Document 1 discloses a method for detecting the speed by using the rising edge and the falling edge of the output pulse of the encoder. The prior art will be briefly described below.

FIG. 6 is a configuration diagram of the prior art described in Patent Document 1. In FIG.
In FIG. 6, the latch signal generating unit 21 detects the rising edge and the falling edge from two types of pulses having different phases of A phase and B phase output from the encoder, and a total of four types of latch signals ED0. Create ED3. The angle measurement counter 22 performs UP / DOWN of the counter using the latch signal (4F) and the UP / DOWN signal indicating the rotation direction of the electric motor.

The time measurement counter 23 is a down counter that becomes zero in synchronization with the speed calculation cycle. Corresponding to each of the four types of latch signals ED0 to ED3, the first data latch 24-1 to 24-4 that latches and stores the value of the angle measurement counter 22, and the value of the time measurement counter 23 are latched. Second data latches 25-1 to 25-4 for storing are provided, and angle data latches 27-1 to 27-4 and time data latches 28-1 to 28-4 that latch input data every speed calculation cycle. Is provided.
The CPU 30 reads the angle measurement values (values of the data latches 27-1 to 27-4) and the time measurement values (values of the data latches 28-1 to 28-4) for each speed calculation cycle, and the electric motor according to the flowchart described later. Detect the speed of.

  Reference numeral 26 denotes an edge holding unit that detects and holds edge changes of the A-phase pulse and B-phase pulse from the latch signals ED0 to ED3, and 29 denotes an edge change from the output signals FIL0 to FIL3 of the edge holding unit 26. An edge change information holding unit for holding edge change information by setting and holding “1” if there is even one change and “0” if there is no change once, 31 is a controller, and 32 is third data. Indicates a latch.

FIG. 7 is a flowchart showing the speed detection operation according to the conventional technique.
The edge holding unit 26 in FIG. 6 detects the presence or absence of an edge change for each speed calculation cycle, and the CPU 30 reads the output values F0 to F3 of the edge change information holding unit 29 latched for each speed calculation cycle. If the edge is detected even once in the speed calculation cycle, the latest edge is searched from the magnitude of the count value, and the angle measurement values of the data latches 27-1 to 27-4 corresponding to the latest edge and the data latches 28-1 to 28-1 are searched. The speed ω is calculated based on Equation 1 using the time measurement value 28-4.

However, theta _New angle measurement value read in this sample timing, theta _OLD angle measurement value read at the previous sampling timing, T _S is the sampling period (control period), T _New is read in this sample timing The time measurement value, T _OLD, is the time measurement value read at the previous sample timing.
Further, if the pulse did not exist even once the speed calculation cycle, to estimate the rate of addition of the sampling period T _S to T _OLD.

This speed detection method according to the prior art has the following problems.
(1) Since the number of output pulses of the encoder is measured by the angle measurement counter 22, the angle measurement counter 22 overflows and the speed cannot be detected in a high speed region where there are a large number of pulses for each speed calculation cycle. There is.
(2) In order to prevent the angle measurement counter 22 from overflowing with respect to the problem (1), if an allowance is provided in the measurable range of the angle measurement counter 22, the storage capacity increases and the cost of the control device increases. To do.
(3) Since the number of pulses of the encoder attached to the motor varies from several hundreds to several hundreds of thousands, some of the encoders cannot be used due to the limitations of the angle measurement counter 22 described in (1) and (2) above. is there. That is, the speed detection method according to Patent Document 1 has a limitation in versatility.

As a conventional technique for solving the above-described problems, a speed detection device according to Patent Document 2 is known. Hereinafter, the configuration and operation of the speed detection device will be described with reference to FIGS.
FIG. 3 shows the configuration of the speed detection device according to Patent Document 2. The latch signal creation unit 21 serving as edge detection means includes an A-phase pulse with different phases output from an encoder (not shown), B The rising and falling edges of the phase pulse are detected, and latch signals ED0, ED1, ED2, and ED3 are created.

  The encoder is connected to, for example, an electric motor rotation shaft, and outputs a number of A-phase pulses and B-phase pulses in proportion to the rotation speed. These output pulses are not limited to two phases of A phase and B phase, but may be three or more phases, but here, the rising edge and the rising edge of the A phase pulse and B phase pulse output from the two phase encoder are used. A case where the velocity is detected using four types of falling edges will be described.

The A-phase pulse and the B-phase pulse are also input to the rotation direction detection unit 32. The rotation direction detection unit 32 detects the rotation direction (CW: forward rotation, CCW: reverse rotation) of the motor from the A phase pulse, the B phase pulse, and the latch signals ED0, ED1, ED2, and ED3.
The signal CW / CCW output from the rotation direction detection unit 32 is input to the rotation direction holding unit 33, is latched by a speed calculation period signal (sampling signal) SMPL, and is output as a rotation direction detection signal CWDET.

The latch signals ED0, ED1, ED2, and ED3 are input to the data latches 25-1 to 25-4 as time storage means and are also input to the edge holding unit 26.
The data latches 25-1 to 25-4 receive the time measurement values T _{DE0EN to} T _DE3EN output from the time measurement counter 23, and these time measurement values T are received by latch signals ED0, ED1, ED2, and ED3. _{DE0EN to TDE3EN} are stored and sent to the data latches 28-1 to 28-4 in the next stage. The time measurement counter 23 is a down counter that becomes zero in synchronization with the speed calculation cycle.
The data latches 28-1 to 28-4 send the time measurement values T _{DE0EN to} T _DE3EN latched by the speed calculation cycle signal SMPL to the CPU 30 as the time measurement values T _{0EN to} T _3EN .

  The latch signals ED0, ED1, ED2, and ED3 are input to the edge holding unit 26 including a J-K flip-flop, and the presence / absence of a change in each edge in the speed calculation cycle is detected. The edge holding unit 26 sets and holds “1” for each latch signal ED0, ED1, ED2, and ED3 if the edge changes even once, and sets “0” if there is no change. Hold. These held data are sent to the edge change information holding unit 29, latched by the speed calculation cycle signal SMPL, and sent to the CPU 30 as edge change detection signals EDF0 to EDF3.

FIG. 4 is a timing chart showing the operation of the rotation direction detector 32. The rotation direction detector 32 detects the rotation direction from the state of the A-phase pulse and the B-phase pulse when the latch signals ED0, ED1, ED2, and ED3 are generated.
In FIG. 4, for example, when the rising edge of the A-phase pulse is detected by the signal ED0 at time (3) (ED0 is “1”), when the B-phase pulse is not detected (B-phase pulse is “0”), It is determined that the rotation is normal, and a signal CW (= “1”) is output. On the other hand, when the falling edge of the B phase pulse is detected by the signal ED3 at the time point (4) (ED3 is “1”), when the A phase pulse is detected (the A phase pulse is “1”), It is determined that the rotation is reverse, and a signal CCW (= “0”) is output.
The rotation direction detection signal thus obtained is latched by the speed calculation period signal SMPL in the rotation direction holding unit 33 and sent to the CPU 30 as the rotation direction detection signal CWDET.
In FIG. 4, T _CHNG indicates a point in time when the rotation direction changes.

In the CPU 30, the time measurement values T _{0EN to} T 3EN from the data latches 28-1 to _28-4 , the rotation direction detection signal CWDET from the rotation direction holding unit 33, and the edge change information holding unit 29 for each speed calculation cycle. The speed of the motor is detected using the edge change detection signals EDF0 to EDF3.

FIG. 5 is a timing chart showing the speed detection operation. Here, as an example, description will be made assuming that the speed is detected at the sample timing (timing of the speed calculation cycle signal SMPL) at the time point (1) in FIG.
At the time (1) in FIG. 5, according to the illustrated sample timing, the latest edge is the rising edge of the A-phase pulse by the signal ED0. This is determined from the edge change detection signals EDF0 to EDF3 because EDF0 is “1” and the other EDF1 to EDF3 are “0”. Here, in FIG. 5, only the value of EDF0 is illustrated, and EDF1 to EDF3 are omitted.

  When a plurality of edge change detection signals EDF0 to EDF3 are “1”, the one with the smallest corresponding time measurement value is regarded as the latest edge. This is because the time measurement counter 23 is a down counter that becomes zero at the sample timing, and the time measurement value corresponding to the latest edge is close to zero. Of course, an up-counter may be used as the time measurement counter 23. In this case, it is only necessary to regard the one having the maximum corresponding time measurement value as the latest edge.

Therefore, the time measurement value T _DE0EN = T _0EN1 latched by the signal _ED0 is the latest time measurement value (current value), and the time measurement value T _DE0EN = T _0EN0 when the previous signal ED0 is generated is the previous value. use. The value of T _0EN0 cannot be read from the data latch 28-1 at the time (1), but is stored in the memory in the CPU 30 at the time (1) ′ when the previous edge change detection signal EDF0 is “1”. It is possible to use it by keeping it.
In addition, the maximum value of the time measurement counter 23 corresponding to the speed calculation cycle is set to T _max, and the number of samplings in which EDF 0 was zero between the previous value T _0EN0 and the current value T _0EN 1 is set to N ₀ , and these are set in the CPU 30. The speed n is calculated on the basis of Formula 2 after being stored in the memory.

In Equation 2, CW _sign indicates a rotation direction, and forward rotation (CW) is “1” and reverse rotation (CCW) is “−1”. K is a constant related to the number of output pulses per rotation of the encoder.

JP-A-6-1118090 (paragraphs [0024] to [0043], FIG. 2, FIG. 14 etc.) JP 2009-85716 A (paragraphs [0019] to [0033], FIGS. 1 to 3)

The prior art according to Patent Document 2 described above has the following problems.
In other words, when detecting the speed of the motor driven by the power converter, in the high speed range where the output pulses of the encoder are dense, the calculation cycle of the speed detection value is delayed when calculating the phase of the output voltage of the power converter. Phase lag occurs. In particular, when a permanent magnet synchronous motor or the like is driven, an error with the magnetic flux axis of the permanent magnet occurs, resulting in a torque control error. If a torque error occurs in this way, the current flowing through the motor increases, the loss of the motor increases, and the efficiency may decrease, which is not preferable.

Hereinafter, the reason why the above-described phase delay occurs will be described in detail.
FIG. 8 is a configuration diagram of a general speed control system. In the figure, 101 and 103 are subtraction means, 102 is speed control means, 104 is current control means, 105 and 107 are coordinate conversion means, and 106 is speed detection means.

As shown in the figure, the speed control system can be simply expressed as a speed control system that calculates a torque command or a current command from the deviation between the speed command and the detected detection value, and a voltage command from the deviation between the current command and the current detection value. It comprises a current control system for calculating, and a coordinate conversion means for converting the voltage command and the current detection value.
The speed control system and the current control system have different time constants for the target motor (the speed control system has a mechanical system time constant and is several times slower than the electrical time constant of the current control system). Calculations are performed with different periods. According to the method of changing the control cycle in this way, the calculation load of the microprocessor or the like can be distributed to reduce the cost of the control device, and thus is widely used. Generally, the control cycle of the speed control system (corresponding to the speed calculation cycle signal SMPL described above) is designed to be 4 to 10 times the control cycle of the current control system.

  Here, the coordinate conversion means 105 and 107 perform coordinate conversion using the phase of current or voltage. This phase is obtained by integrating the speed, but if the speed detection value calculated by the control period of the speed control system is integrated as described above, the time is delayed with respect to the control period of the current control system. Particularly in the high-speed region, the phase shift becomes relatively large with respect to the time delay. Therefore, when accurately controlling the magnetic flux position of a permanent magnet synchronous motor, etc. Deviation occurs between the magnetic flux position.

In order to cope with the above problem, when a function for holding the edges of the A-phase pulse and the B-phase pulse in the current control cycle is added to the configuration of FIG. 3, a double holding circuit and memory are stored for each edge. Capacity is required, which increases the cost of the control device.
Therefore, the problem to be solved by the present invention is to control a motor that prevents a phase shift particularly in a high speed range and enables high-accuracy speed control by adding a minimum circuit to the prior art related to Patent Document 2. To provide an apparatus.

In order to solve the above problems, an invention according to claim 1 is a control device for an electric motor driven at a variable speed by a power converter,
Speed at which the motor current command is generated by calculating the rotation speed of the motor from the output pulse of the encoder attached to the motor and performing speed control according to the first control cycle so that the detected speed value matches the speed command. A control system;
A current control system that generates an output voltage command of the power converter by performing current control according to a second control cycle that is shorter than the first control cycle so that the current detection value of the motor matches the current command;
Means for converting the output voltage command and the current detection value using the output voltage phase of the power converter, and a control device comprising:
Edge detection means for detecting an edge of the output pulse;
Rotation direction detection means for detecting the rotation direction of the electric motor based on the detected edge;
Time measuring means for measuring time synchronized with the first control cycle;
Time storage means for holding the time measurement value of the time measurement means by the output of the edge detection means;
Edge change information holding means for detecting a change state of the edge within the first control cycle and holding it as edge change information;
A calculation means for calculating the rotation speed of the electric motor using the rotation direction, the time measurement value, and the edge change information held for each first control period;
Counting means for counting the number of at least one of the edges of the output pulse;
Holding means for holding the count value by the counting means for each second control period;
First phase calculation means for calculating the output voltage phase from the count value held by the holding means.

The invention according to claim 2 is the motor control device according to claim 1,
Furthermore, it comprises a second phase calculation means for calculating the output voltage phase from the speed detection value calculated by the first control cycle, and when the motor rotation speed is low, the first phase calculation means When the rotational speed of the electric motor is high, the output voltage phase is calculated by the second phase calculating means.

  According to the present invention, even when an electric motor is driven in a high speed range, a phase shift due to a calculation delay can be prevented, and highly accurate speed control can be realized over a wide speed range from low speed to high speed. is there.

It is a block diagram which shows the principal part of the control apparatus which concerns on embodiment of this invention. It is a conceptual diagram of the function which selects the movement amount of a phase. It is a block diagram which shows the speed detection apparatus which concerns on patent document 2. FIG. It is a timing chart which shows operation | movement of the rotation direction detection part in FIG. It is a timing chart which shows the speed detection operation in FIG. It is a block diagram which shows the prior art described in patent document 1. 10 is a flowchart showing a speed detection operation according to the conventional technique described in Patent Document 1. It is a block diagram of a general speed control system.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a speed detection device as a main part of a control device according to this embodiment. The same components as those in FIG. The explanation will focus on the part.

  First, a first embodiment of the present invention corresponding to claim 1 is directed to at least one edge among rising edges or falling edges of an A-phase pulse and a B-phase pulse (in the example of FIG. 1, the rising edge of an A-phase pulse). Is counted by the counter 41, and this count value is a cycle shorter than the control cycle of the speed control system (referred to as the first control cycle for convenience) (for example, the control cycle of the current control system). The speed calculation period signal (sampling signal) SMPL2 of the second control period for convenience is held in the latch 42 and sent to the CPU 30, and the CPU 30 calculates the phase used for coordinate conversion from the count value. There is a feature.

数式３において、Ｋ_ｅはエンコーダの１回転あたりのパルス数であり、ｐは電動機の極対数を示している。
この数式３によれば、例えば、極対数ｐが２の電動機を対象とした時にラッチ４２から入力されるカウント値Ｎが１０２４であり、電流制御系の制御周期の間でエッジを１回検出した場合は、移動量Δθが０．０１２２７〔ｒａｄ〕、すなわち０．０１２２７〔ｒａｄ〕だけ位相が進んだことを意味する。 In the CPU, the count value input from the latch 42 is set to N, and the movement amount Δθ from the phase in the previous control cycle is obtained by Equation 3.

In Equation 3, _Ke is the number of pulses per revolution of the encoder, and p is the number of pole pairs of the motor.
According to Equation 3, for example, the count value N input from the latch 42 is 1024 when an electric motor having a pole pair number p of 2 is targeted, and an edge is detected once during the control cycle of the current control system. In this case, the movement amount Δθ is 0.01227 [rad], that is, the phase is advanced by 0.01227 [rad].

ここで、θ_ｎ＋１は回転方向が正の場合はΔθを加算し、負の場合はΔθを減算して求める。 Assuming that the phase in the previous control cycle is θ _n , the phase θ _{n + 1} at the current sampling time is obtained by Equation 4.

Here, θ _{n + 1} is obtained by adding Δθ when the rotation direction is positive, and subtracting Δθ when the rotation direction is negative.

Note that the counter 41 used in this embodiment has the same function as the edge number measuring means in Patent Document 1 described above in that it counts the number of edges of a pulse. However, Patent Document 1 discloses nothing about the phase calculation method of Equation 4 (phase calculation method in the current control system) based on the difference in control cycle between the current control system and the speed control system.
Further, in this embodiment, it is only necessary to detect at least one of the rising edge or the falling edge of the A-phase pulse and the B-phase pulse. It can be easily realized simply by adding and changing the contents of calculation by the CPU 30.

数式５では、数式２により速度制御系の制御周期で演算した速度検出値ｎを、電流制御系の制御周期Ｔ_Ｓにより積分してΔθを求めている。従って、速度制御系の制御周期で演算した速度検出値ｎが電流制御系の制御周期Ｔ_Ｓにおいて一定であるという前提で平均化して演算していることになる。
すなわち、電流制御系の制御周期で変化が起こったときに、数式３では次の電流制御系の制御周期で位相の変化を演算することができるが、数式５によれば、速度制御系の制御周期で速度検出値ｎの変化が起きてから、電流制御系の制御周期で平均化するため、制御周期の差による時間遅れが数式３に対して大きくなる。 Next, the reason why the phase delay can be improved as compared with Patent Document 2 in this embodiment will be described.
In Patent Document 2, the phase of the current control system is not mentioned, but in general, the phase movement amount Δθ can be calculated by Equation 5 from the relationship between the speed and the angle.

In Equation 5, the speed detection value n calculated in the control period of the speed control system according to Equation 2, seeking Δθ by integrating the control period T _S of the current control system. Therefore, will have been computed by averaging the assumption that constant is in the control period T _S of the speed detection value n is the current control system which is calculated by the control period of the speed control system.
That is, when a change occurs in the control cycle of the current control system, the change in phase can be calculated in the next control cycle of the current control system in Equation 3, but according to Equation 5, the control of the speed control system can be calculated. Since the speed detection value n changes in the cycle and is averaged in the control cycle of the current control system, the time delay due to the difference in the control cycle becomes larger than that in Equation 3.

  Particularly in the high-speed region, a plurality of edges are detected from the encoder output pulse during the control period of the current control system, so that the phase shift due to the time delay becomes relatively large. If the phase shift is large, a wasteful current must be supplied to the actual torque, which causes problems such as increased loss.

  Therefore, the second embodiment of the present invention has been made to solve the above problems. This embodiment corresponds to the invention according to claim 2, but only the software processing in the CPU 30 is different from that of the first embodiment, and the configuration of the entire control device is the same as that of FIG.

FIG. 2 shows the selection function of the phase movement amount Δθ in the second embodiment. As described above, the result of calculating Δθ by the equation 3 using the edge count value N is Δθ _A , and the speed detection value n Let Δθ _B be the result of calculating Δθ by Equation 5 using
Since the count value N is 1 or more in the high-speed region, Δθ _A is selected by the switching means 51 in order to set Δθ to be substituted into Equation 4 to Equation 3. On the other hand, in the low speed region, N may be 0, and in Equation 3, Δθ becomes zero and there is no phase change. However, since the actual speed may not be zero, Δθ _B is selected by the switching means 51 in order to set Δθ to be substituted into Equation 4 to Equation 5.

That is, in this embodiment, the phase movement amount Δθ is selected according to the speed range, and since Equation 3 and Equation 5 have the same value on average, there is no significant variation when switching by the switching means 51. It is possible to switch smoothly.
As described above, according to the present embodiment, by obtaining the phase in consideration of the control cycle of the current control system in accordance with the speed range of the motor, there is no phase shift and high-accuracy speed control from the low speed range to the high speed range. It can be performed.

21: Latch signal creation unit 23: Time measurement counter 25-1 to 25-4: Data latch 26: Edge holding unit 28-1 to 28-4: Data latch 29: Edge change information holding unit 30: CPU
31: Controller 32: Rotation direction detection unit 33: Rotation direction holding unit 41: Counter 42: Latch 51: Switching unit 101, 103: Subtraction unit 102: Speed control unit 104: Current control unit 105, 107: Coordinate conversion unit 106: Speed detection means

Claims (2)

A control device for an electric motor driven at a variable speed by a power converter,
Speed at which the motor current command is generated by calculating the rotation speed of the motor from the output pulse of the encoder attached to the motor and performing speed control according to the first control cycle so that the detected speed value matches the speed command. A control system;
A current control system that generates an output voltage command of the power converter by performing current control according to a second control cycle that is shorter than the first control cycle so that the current detection value of the motor matches the current command;
Means for converting the output voltage command and the current detection value using the output voltage phase of the power converter;
In a control device comprising:
Edge detection means for detecting an edge of the output pulse;
Rotation direction detection means for detecting the rotation direction of the electric motor based on the detected edge;
Time measuring means for measuring time synchronized with the first control cycle;
Time storage means for holding the time measurement value of the time measurement means by the output of the edge detection means;
Edge change information holding means for detecting a change state of the edge within the first control cycle and holding it as edge change information;
A calculation means for calculating the rotation speed of the electric motor using the rotation direction, the time measurement value, and the edge change information held for each first control period;
Counting means for counting the number of at least one of the edges of the output pulse;
Holding means for holding the count value by the counting means for each second control period;
First phase calculating means for calculating the output voltage phase from the count value held by the holding means;
An electric motor control device comprising: In the motor control device according to claim 1,
And a second phase calculating means for calculating the output voltage phase from the speed detection value calculated by the first control period,
The output voltage phase is calculated by the first phase calculation means when the rotation speed of the motor is low, and by the second phase calculation means when the rotation speed of the motor is high. Control device.

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